Fractal Characterization Of Seepage-Pores Of Coals From China: An Investigation To Permeability Of Coals

To better understand the seepage-pores (pore diameter larger than 100 nanometers) characteristics of coals and their influence on the permeability of coals, we have conducted fractal analyses for 34 fresh coal samples (mean maximum vitrinite reflectance R-o from 0.43% to 4.21%) from North-, Northwest- and Northeast China. Analyzing the data from mercury porosimetry indicates that coals are fractal at the pore diameter ranging from 0.1 to 500 mu m. The values of calculated fractal dimensions are from 2.61 to 2.98.The fractal dimension has a negative correlation with the petrologic permeability of coals, and this relationship is particularly fitted well for higher rank coals (coals with 1.47-4.21% R-o) where a strong negative linear correlation (r(2)=0.85) is observed. Further investigation indicates that fractals of coals are essentially related to rank, component, and pore structure of coals. Fractal dimensions changes versus coal rank show the 'U-shaped' trend, with a minimum occurring in the 1.1-1.3 % R-o. The sub-bituminous, high volatile bituminous, semi-anthracite and anthracite have higher fractal dimensions. It is suggested that the effects of rank upon fractal dimensions are mainly due to the variety of micropores contents and moisture contents during the coalification process.